Seroepidemiology: an underused tool for designing and monitoring vaccination programmes in low- and middle-income countries

Seroprevalence of measles antibodies and factors associated with susceptibility: a national survey in Mexico using a plaque reduction neutralization test

Measles continues to be one of the leading causes of child mortality worldwide, even though a highly effective vaccine has existed for more than 40 years. We aimed to describe the seroprevalence of measles antibodies in Mexico in 2012 and the risk factors associated with susceptibility. A total of 7,785 serum samples were analyzed from the National Health and Nutrition Survey in Mexico. This national survey is representative of the general population, including noninstitutionalized adult, adolescent, and child populations. Antibody titers were classified into protective (> 120 mIU/mL) or susceptible (≤ 120 mIU/mL) levels. The weighted seroprevalence and susceptibility of the overall population were 99.37% (95% CI 99.07–99.58) and 0.63% (95% CI 0.42–0.93), respectively. Among 1-to-4-year-old children, 2.18% (95% CI 1.36–3.48) were susceptible to measles. Among adolescents and young adults, the prevalence of susceptibility was as follows: those 15–19 years of age had a prevalence of 0.22% (95% CI 0.09–0.57), and those 30–39 years of age had a prevalence of 1.17% (95% CI 0.47–2.85). Susceptibility was associated with young age, living in Mexico City, living in crowded households and unknown or nonvaccinated status among 1- to 5-year-old children. Although the overall sample population seroprevalence for measles is above 95%, increased susceptibility among younger children signals the importance of the timely administration of the first vaccine dose at 12 months of age. Furthermore, increased susceptibility among specific subgroups indicates the need to reinforce current vaccination policies, including the immunization of unvaccinated or incompletely vaccinated individuals from 10 to 39 years of age.

Dried blood spot cards: A reliable sampling method to detect human antibodies against rabies virus

Background

Although preventable by vaccination for more than a century, rabies virus still causes numerous fatalities every year. To determine antibody levels in humans, blood collected with a finger prick and applied on dried blood spot (DBS) cards is an alternative for venipuncture. The use of DBS is specifically valuable in remote areas, as it is easy to perform, store and transport. Therefore, the technique is frequently used for epidemiological studies of tropical diseases. Up to present, determination of rabies virus antibody levels on human DBS has not been validated.

Methodology/Principal findings

We evaluated the use of human DBS for rabies serology and analyzed 99 pre- or post-vaccination serum and DBS samples with a fluorescent antibody virus neutralization test (FAVNt), which is the gold standard to detect protective antibody levels, and a Bio-Rad Platelia Rabies II ELISA. Sensitivity and specificity of DBS eluates tested with the FAVNt were 97% and 92%, respectively and 87% and 96% when tested with the Platelia-II ELISA. Antibody levels measured in serum with the FAVNt, correlated best with antibody levels measured in DBS with the FAVNt (R = 0.88).

Conclusions/Significance

This is the first study that applies DBS for reliable detection of human antibodies against rabies virus. Both the FAVNt and Platelia-II ELISA demonstrate an acceptable performance on DBS, providing opportunities for rabies serology in remote areas. This technique could drastically ease studies evaluating (novel) rabies vaccination strategies and monitoring persisting immunity in humans at risk, living in rabies endemic regions.

Rabies is a nearly 100% fatal disease in humans. However, available vaccines are effective in preventing rabies infection. To investigate if a person is protected against rabies, rabies virus neutralizing antibody levels in the blood are determined. The World Health Organization defines protective immunity as a rabies virus antibody concentration of at least 0.5 IU/ml detected in serum using a virus neutralization test. Yet, in remote areas serum may be rather difficult to collect, process and transport. Whole blood collected with a finger prick and applied on filter paper cards, also known as dried blood spots (DBS), are an easier alternative. This collection method is frequently used for serology of several tropical infectious diseases, but never studied for rabies serology in humans. Therefore, we compared antibody levels measured in serum with those measured in DBS eluates, using the gold standard FAVNt and related it to another commonly used test for human rabies serology, the Platelia-II ELISA. We found that both assays had a good performance on DBS eluates. The reported high specificities provide confidence that unprotected individuals will rarely be missed. Therefore, the DBS is a promising sampling technique for evaluations of vaccination strategies and monitoring persisting immunity after vaccination in populations at risk for rabies.

Neutralizing antibody against SARS-CoV-2 spike in COVID-19 patients, health care workers and convalescent plasma donors: a cohort study using a rapid and sensitive high-throughput neutralization assay

Rapid and specific antibody testing is crucial for improved understanding, control, and treatment of COVID-19 pathogenesis. Herein, we describe and apply a rapid, sensitive, and accurate virus neutralization assay for SARS-CoV-2 antibodies. The new assay is based on an HIV-1 lentiviral vector that contains a secreted intron Gaussia luciferase or secreted Nano-luciferase reporter cassette, pseudotyped with the SARS-CoV-2 spike (S) glycoprotein, and is validated with a plaque reduction assay using an authentic, infectious SARS-CoV-2 strain. The new assay was used to evaluate SARS-CoV-2 antibodies in serum from individuals with a broad range of COVID-19 symptoms, including intensive care unit (ICU) patients, health care workers (HCWs), and convalescent plasma donors. The highest neutralizing antibody titers were observed among ICU patients, followed by general hospitalized patients, HCWs and convalescent plasma donors. Our study highlights a wide phenotypic variation in human antibody responses against SARS-CoV-2, and demonstrates the efficacy of a novel lentivirus pseudotype assay for high-throughput serological surveys of neutralizing antibody titers in large cohorts.

Measles and rubella IgG seroprevalence in persons 6 month-35 years of age, Mongolia, 2016

BACKGROUND

In 2015-2016, Mongolia experienced an unexpected large measles outbreak affecting mostly young children and adults. After two nationwide vaccination campaigns, measles transmission declined. To determine if there were any remaining immunity gaps to measles or rubella in the population, a nationally representative serosurvey for measles and rubella antibodies was conducted after the outbreak was over.

METHODS

A nationwide, cross-sectional, stratified, three-stage cluster serosurvey was conducted in November-December 2016. A priori, four regional strata (Ulaanbaatar, Western, Central, and Gobi-Eastern) and five age strata (6 months-23 months, 2-7 years, 8-17 years, 18-30 years, and 31-35 years) were created. Households were visited, members interviewed, and blood specimens were collected from age-appropriate members. Blood specimens were tested for measles immunoglobulin G (IgG) and rubella IgG (Enzygnost® Anti-measles Virus/IgG and Anti-rubella Virus/IgG, Siemens, Healthcare Diagnostics Products, GmbH Marburg, Germany). Factors associated with seropositivity were evaluated.

RESULTS

Among 4598 persons aged 6 months to 35 years participating in the serosurvey, 94% were measles IgG positive and 95% were rubella IgG positive. Measles IgG seropositivity was associated with increasing age and higher education. Rubella IgG seropositivity was associated with increasing age, higher education, smaller household size, receipt of MMR in routine immunization, residence outside the Western Region, non-Muslim religious affiliation, and non-Kazakh ethnicity. Muslim Kazakhs living in Western Region had the lowest rubella seroprevalence of all survey participants.

CONCLUSIONS

Nationally, high immunity to both measles and rubella has been achieved among persons 1-35 years of age, which should be sufficient to eliminate both measles and rubella if future birth cohorts have ≥ 95% two dose vaccination coverage. Catch-up vaccination is needed to close immunity gaps found among some subpopulations, particularly Muslim Kazakhs living in Western Region.

An open source tool to infer epidemiological and immunological dynamics from serological data: serosolver

We present a flexible, open source R package designed to obtain biological and epidemiological insights from serological datasets. Characterising past exposures for multi-strain pathogens poses a specific statistical challenge: observed antibody responses measured in serological assays depend on multiple unobserved prior infections that produce cross-reactive antibody responses. We provide a general modelling framework to jointly infer infection histories and describe immune responses generated by these infections using antibody titres against current and historical strains. We do this by linking latent infection dynamics with a mechanistic model of antibody kinetics that generates expected antibody titres over time. Our aim is to provide a flexible package to identify infection histories that can be applied to a range of pathogens. We present two case studies to illustrate how our model can infer key immunological parameters, such as antibody titre boosting, waning and cross-reaction, as well as latent epidemiological processes such as attack rates and age-stratified infection risk.

Serological Approaches for COVID-19: Epidemiologic Perspective on Surveillance and Control

Since December 2019, the novel coronavirus, SARS-CoV-2, has garnered global attention due to its rapid transmission, which has infected more than two million people worldwide. Early detection of SARS-CoV-2 is one of the crucial interventions to control virus spread and dissemination. Molecular assays have been the gold standard to directly detect for the presence of viral genetic material in infected individuals. However, insufficient viral RNA at the point of detection may lead to false negative results. As such, it is important to also employ immune-based assays to determine one's exposure to SARS-CoV-2, as well as to assist in the surveillance of individuals with prior exposure to SARS-CoV-2. Within a span of 4 months, extensive studies have been done to develop serological systems to characterize the antibody profiles, as well as to identify and generate potentially neutralizing antibodies during SARS-CoV-2 infection. The vast diversity of novel findings has added value to coronavirus research, and a strategic consolidation is crucial to encompass the latest advances and developments. This review aims to provide a concise yet extensive collation of current immunoassays for SARS-CoV-2, while discussing the strengths, limitations and applications of antibody detection in SARS-CoV-2 research and control.

A systematic review of the agreement of recall, home-based records, facility records, BCG scar, and serology for ascertaining vaccination status in low and middle-income countries

Background: Household survey data are frequently used to estimate vaccination coverage - a key indicator for monitoring and guiding immunization programs - in low and middle-income countries. Surveys typically rely on documented evidence from home-based records (HBR) and/or maternal recall to determine a child's vaccination history, and may also include health facility sources, BCG scars, and/or serological data. However, there is no gold standard source for vaccination history and the accuracy of existing sources has been called into question. Methods and Findings: We conducted a systematic review of literature published January 1, 1975 through December 11, 2017 that compared vaccination status at the child-level from at least two sources of vaccination history. 27 articles met inclusion criteria. The percentage point difference in coverage estimates varied substantially when comparing caregiver recall to HBRs (median: +1, range: -43 to +17), to health facility records (median: +5, range: -29 to +34) and to serology (median: -20, range: -32 to +2). Ranges were also wide comparing HBRs to facility-based records (median: +17, range: -61 to +21) and to serology (median: +2, range: -38 to +36). Across 10 studies comparing recall to HBRs, Kappa values exceeded 0.60 in 45% of comparisons; across 7 studies comparing recall to facility-based records, Kappa never reached 0.60. Agreement varied depending on study setting, coverage level, antigen type, number of doses, and child age. Conclusions: Recall and HBR provide relatively concordant vaccination histories in some settings, but both have poor agreement with facility-based records and serology. Long-term, improving clinical decision making and vaccination coverage estimates will depend on strengthening administrative systems and record keeping practices. Short-term, there must be greater recognition of imperfections across available vaccination history sources and explicit clarity regarding survey goals and the level of precision, potential biases, and associated resources needed to achieve these goals.

Seroprevalence of Bordetella pertussis toxin antibodies in children and adolescents in Tunis, Tunisia

Pertussis remains a public health concern in most countries. This cross-sectional study aims to investigate the distribution of pertussis toxin antibodies (anti-PT IgG) in Tunisian children and adolescents aged 3–18 years, to define optimal age for booster vaccination. Anti-PT IgG concentrations of enrolled participants were measured using commercial enzyme-linked immunosorbent assay. Concentrations were classified as: indicative of current/recent infection if ⩾100 IU/ml, indicative of recent exposure to Bordetella pertussis within the last year if 40–100 IU/ml and less likely revealing a recent exposure to B. pertussis if <40 IU/ml. Between March and June 2018, a total of 304 participants (mean age: 9.3 years) were included in this study. Overall, 12.8% (95% confidence interval (CI) 9.1%–16.6%) were seropositive (IgG levels ⩾40 IU/ml). Among them, 14.7% (95% CI 2.3%–23.3%) had levels indicative of a current/recent infection. The multivariate Poisson regression analysis suggested associations between female gender, as well as age group 13–18 years and 3–5 years and higher anti-PT IgG concentrations. Our results are consistent with the notion that vaccine-induced immunity decline, as well as circulation of pertussis among school children and adolescents enables them to be reservoirs of infection and disease transmission to vulnerable infants. Booster dose of acellular pertussis vaccine for school entrants is therefore recommended.

Global trends in measles publications

INTRODUCTION

Beginning with the 1960s, this review analyzes trends in publications on measles indexed by the National Library of Medicine from January 1960 to mid-2018. It notes both the growth in numbers of published papers, and the increasing number and proportion of publications, in the current century, of articles on such items as costing, measles elimination, and determinants of coverage.

METHODS

A two-person team extracted from the National Library of Medicine (NLM) homepage all citations on measles beginning in 1960 and continuing through mid-2018. These were then classified both by overall number and by subject matter, with tabular summaries of both by decade and by subject matter. The tabular presentation forms the basis for a discussion of the ten most frequently cited subjects, and publication trends, with a special emphasis on the current century.

RESULTS

As in the past, the most often currently published items have been on coverage and its determinants, measles elimination, outbreak reports, SSPE, and SIAs. The putative relationship between vaccination and autism saw a spurt of articles in the 1990s, rapidly declining after the IOM report rejecting the causative hypothesis.

CONCLUSION

There is a discussion on the sequencing of polio and measles eradication, the former unlikely before 2022, and an examination of likely research priorities as the world moves from measles control to measles eradication. There is a key role for social science in combatting vaccination reticence. The role of technical innovations, such as micropatch vaccination, is discussed.

A systematic review of the agreement of recall, home-based records, facility records, BCG scar, and serology for ascertaining vaccination status in low and middle-income countries

Background: Household survey data are frequently used to estimate vaccination coverage - a key indicator for monitoring and guiding immunization programs - in low and middle-income countries. Surveys typically rely on documented evidence from home-based records (HBR) and/or maternal recall to determine a child’s vaccination history, and may also include health facility sources, BCG scars, and/or serological data. However, there is no gold standard source for vaccination history and the accuracy of existing sources has been called into question.

Methods and Findings: We conducted a systematic review of literature published January 1, 1975 through December 11, 2017 that compared vaccination status at the child-level from at least two sources of vaccination history. 27 articles met inclusion criteria. The percentage point difference in coverage estimates varied substantially when comparing caregiver recall to HBRs (median: +1, range: -43 to +17), to health facility records (median: +5, range: -29 to +34) and to serology (median: -20, range: -32 to +2). Ranges were also wide comparing HBRs to facility-based records (median: +17, range: -61 to +21) and to serology (median: +2, range: -38 to +36). Across 10 studies comparing recall to HBRs, Kappa values exceeded 0.60 in 45% of comparisons; across 7 studies comparing recall to facility-based records, Kappa never reached 0.60. Agreement varied depending on study setting, coverage level, antigen type, number of doses, and child age.

Conclusions: Recall and HBR provide relatively concordant vaccination histories in some settings, but both have poor agreement with facility-based records and serology. Long-term, improving clinical decision making and vaccination coverage estimates will depend on strengthening administrative systems and record keeping practices. Short-term, there must be greater recognition of imperfections across available vaccination history sources and explicit clarity regarding survey goals and the level of precision, potential biases, and associated resources needed to achieve these goals.

Using models to shape measles control and elimination strategies in low- and middle-income countries: A review of recent applications

After many decades of vaccination, measles epidemiology varies greatly between and within countries. National immunization programs are therefore encouraged to conduct regular situation analyses and to leverage models to adapt interventions to local needs. Here, we review applications of models to develop locally tailored interventions to support control and elimination efforts. In general, statistical and semi-mechanistic transmission models can be used to synthesize information from vaccination coverage, measles incidence, demographic, and/or serological data, offering a means to estimate the spatial and age-specific distribution of measles susceptibility. These estimates complete the picture provided by vaccination coverage alone, by accounting for natural immunity. Dynamic transmission models can then be used to evaluate the relative impact of candidate interventions for measles control and elimination and the expected future epidemiology. In most countries, models predict substantial numbers of susceptible individuals outside the age range of routine vaccination, which affects outbreak risk and necessitates additional intervention to achieve elimination. More effective use of models to inform both vaccination program planning and evaluation requires the development of training to enhance broader understanding of models and where feasible, building capacity for modelling in-country, pipelines for rapid evaluation of model predictions using surveillance data, and clear protocols for incorporating model results into decision-making.

Plans for Nationwide Serosurveillance Network in Vietnam

In recent years, serosurveillance has gained momentum as a way of determining disease transmission and immunity in populations, particularly with respect to vaccine-preventable diseases. At the end of 2017, the Oxford University Clinical Research Unit and the National Institute of Hygiene and Epidemiology held a meeting in Vietnam with national policy makers, researchers, and international experts to discuss current seroepidemiologic projects in Vietnam and future needs and plans for nationwide serosurveillance. This report summarizes the meeting and the plans that were discussed to set up nationwide serosurveillance in Vietnam.

High-throughput malaria serosurveillance using a one-step multiplex bead assay

Background

Serological data indicating the presence and level of antibodies against infectious disease antigens provides indicators of exposure and transmission patterns in a population. Laboratory testing for large-scale serosurveys is often hindered by time-consuming immunoassays that employ multiple tandem steps. Some nations have recently begun using malaria serosurveillance data to make inferences about the malaria exposure in their populations, and serosurveys have grown increasingly larger as more accurate estimates are desired. Presented here is a novel approach of antibody detection using bead-based immunoassay that involves incubating all assay reagents concurrently overnight.

Results

A serosurvey in was performed in Haiti in early 2017 with both sera (n = 712) and dried blood spots (DBS, n = 796) collected for the same participants. The Luminex^® multiplex bead-based assay (MBA) was used to detect total IgG against 8 malaria antigens: PfMSP1, PvMSP1, PmMSP1, PfCSP, PfAMA1, PfLSA1, PfGLURP-R0, PfHRP2. All sera and DBS samples were assayed by MBA using a standard immunoassay protocol with multiple steps, as well a protocol where sample and all reagents were incubated together overnight—termed here the OneStep assay. When compared to a standard multi-step assay, this OneStep assay amplified the assay signal for IgG detection for all 8 malaria antigens. The greatest increases in assay signal were seen at the low- and mid-range IgG titers and were indicative of an enhancement in the analyte detection, not simply an increase in the background signal of the assay. Seroprevalence estimates were generally similar for this sample Haitian population for all antigens regardless of serum or DBS sample type or assay protocol used.

Conclusions

When using the MBA for IgG detection, overnight incubation for the test sample and all assay reagents greatly minimized hands-on time for laboratory staff. Enhanced IgG signal was observed with the OneStep assay for all 8 malaria antigens employed in this study, and seroprevalence estimates for this sample population were similar regardless of assay protocol used. This overnight incubation protocol has the potential to be deployed for large-scale malaria serosurveys for the high-throughput and timely collection of antibody data, particularly for malaria seroprevalence estimates.

The Role of Maternally Acquired Antibody in Providing Protective Immunity Against Nontyphoidal Salmonella in Urban Vietnamese Infants: A Birth Cohort Study

Background

Nontyphoidal Salmonella (NTS) organisms are a major cause of gastroenteritis and bacteremia, but little is known about maternally acquired immunity and natural exposure in infant populations residing in areas where NTS disease is highly endemic.

Methods

We recruited 503 pregnant mothers and their infants (following delivery) from urban areas in Vietnam and followed infants until they were 1 year old. Exposure to the dominant NTS serovars, Salmonella enterica serovars Typhimurium and Enteritidis, were assessed using lipopolysaccharide (LPS) O antigen–specific antibodies. Antibody dynamics, the role of maternally acquired antibodies, and NTS seroincidence rates were modeled using multivariate linear risk factor models and generalized additive mixed-effect models.

Results

Transplacental transfer of NTS LPS–specific maternal antibodies to infants was highly efficient. Waning of transplacentally acquired NTS LPS–specific antibodies at 4 months of age left infants susceptible to Salmonella organisms, after which they began to seroconvert. High seroincidences of S. Typhimurium and S. Enteritidis LPS were observed, and infants born with higher anti-LPS titers had greater plasma bactericidal activity and longer protection from seroconversion.

Conclusions

Although Vietnamese infants have extensive exposure to NTS, maternally acquired antibodies appear to play a protective role against NTS infections during early infancy. These findings suggest that prenatal immunization may be an appropriate strategy to protect vulnerable infants from NTS disease.

Measles and rubella immunity in the population of Bhutan, 2017

BACKGROUND

In 2017, measles elimination was verified in Bhutan, and the country appears to have sufficiently high vaccination coverage to achieve rubella elimination. However, a measles and rubella serosurvey was conducted to find if any hidden immunity gaps existed that could threaten Bhutan's elimination status.

METHODS

A nationwide, three-stage, cluster seroprevalence survey was conducted among individuals aged 1-4, 5-17, and >20 years in 2017. Demographic information and children's vaccination history were collected, and a blood specimen was drawn. Serum was tested for measles and rubella immunoglobulin G (IgG). Frequencies, weighted proportions, and prevalence ratios for measles and rubella seropositivity were calculated by demographic and vaccination history, taking into account the study design.

RESULTS

Of the 1325 individuals tested, 1045 (81%, 95% CI 78%-85%) were measles IgG seropositive, and 1290 (97%, 95% CI 95%-99%) were rubella IgG seropositive. Rubella IgG seropositivity was high in all three age strata, but only 47% of those aged 5-17 years were measles IgG seropositive. Additionally, only 41% of those aged 5-17 years who had documented receipt of two doses of measles- or measles-rubella-containing vaccine were seropositive for measles IgG, but almost all these children were rubella IgG seropositive.

CONCLUSIONS

An unexpected measles immunity gap was identified among children 5-17 years of age. It is unclear why this immunity gap exists; however, it could have led to a large outbreak and threatened sustaining of measles elimination in Bhutan. Based on this finding, a mass vaccination campaign was conducted to close the immunity gap.

Seroepidemiology of Measles, Mumps and Rubella on Bonaire, St. Eustatius and Saba: The First Population-Based Serosurveillance Study in Caribbean Netherlands

The National Immunization Program (NIP) on Bonaire, St. Eustatius and Saba (i.e., Caribbean Netherlands (CN)) includes the measles-mumps-rubella (MMR) vaccine since 1988/89. Seroepidemiological data is an important tool to evaluate the NIP, hence a cross-sectional representative population-based serosurveillance study was conducted for the first time in CN in mid-2017. Participants (n = 1829, aged 0-90 years) donated a blood sample and completed a health-related questionnaire. MMR-specific IgG antibodies were determined using a bead-based multiplex immunoassay and risk factors were analyzed using logistic regression models. Overall seroprevalence was high for measles (94%), but lower for mumps and rubella (both 85%). In NIP eligibles, including women of childbearing age, rubella seroprevalence (88%) exceeded the threshold for protection (85%); however, for measles (89%) this protective level (95%) was not met. MMR seropositivity was lowest in children who became CN resident at 11-17 years of age (especially for measles (72%)), mostly originating from Latin America and other non-Western countries. Interestingly, rubella seroprevalence was lowest in non-NIP eligible adults from Dutch overseas territories and Suriname (75%). Taken together, MMR immunity is generally good in CN, nonetheless some risk groups were identified. Additionally, we found evidence for a unique island epidemiology. In light of recent regional measles outbreaks, disease monitoring remains of utmost importance.

Pertussis and the Minnesota State Fair: Demonstrating a Novel Setting for Efficiently Conducting Seroepidemiologic Studies

Seroepidemiologic studies, which measure serum antibody levels produced in response to infection and/or vaccination, can be valuable tools for gaining insight into population level dynamics of infectious diseases. However, because seroepidemiologic studies are expensive and logistically challenging, they are not routinely conducted for surveillance purposes. We have identified a novel venue, state fairgrounds, in which annual sera samples from a population may be rapidly collected with minimal recruitment expenses. We conducted a pilot pertussis seroepidemiologic study over the course of 3 days at the 2016 Minnesota State Fair to determine if this setting, which hosts nearly 2 million visitors over 12 days each year, is viable for facilitating larger seroepidemiologic studies. A total of 104 adults and children were enrolled to provide a finger stick blood sample for serologic testing and to take a written survey regarding recent cough illness and pertussis vaccination. The survey was used to distinguish between antibodies induced by vaccination and pertussis infection. Elevated antibodies suggestive of recent infection were found among two adults. The prevalence of undetectable antibodies, suggestive of susceptibility, was 72.3% (95% CI 59.6, 85.1%) among 7-17 year olds, 53.8% (95% CI 26.7, 80.9%) among 1-6 year olds, and 23.3% (95% CI 8.2, 38.5%) among adults. Our ability to rapidly enroll participants and collect satisfactory specimens suggests that seroepidemiologic studies with 1000-2000 participants could efficiently be completed over the 12-day course of the Minnesota State Fair. This setting raises the possibility of efficiently conducting annual population-based seroepidemiologic studies to supplement traditional public health surveillance in estimating disease prevalence, monitoring vaccine impact, and identifying at-risk groups.

Field Test and Validation of the Multiplier Measles, Mumps, Rubella, and Varicella-Zoster Multiplexed Assay System in the Democratic Republic of the Congo by Using Dried Blood Spots

The critical evaluation of immunization programs is key to identifying areas of suboptimal vaccination coverage, monitoring activities, and aiding development of public health policy. For evaluation of vaccine effectiveness, direct antibody binding assay methods, including enzyme immunoassay, enzyme-linked fluorescence assays, and indirect immunofluorescence assay, are most commonly used for detection of IgG antibodies. However, despite their well-demonstrated, reliable performance, they can be labor-intensive and time-consuming and require separate assays for each individual marker. This necessitates increased sample volumes, processing time, and personnel, which may limit assessment to a few key targets in resource-limited settings, that is, low- and middle-income locations where funding for public health or general infrastructure that directly impacts public health is restricted, limiting access to equipment, infrastructure, and trained personnel. One solution is a multiplexed immunoassay, which allows for the detection of multiple analytes in a single reaction for increased efficiency and rapid surveillance of infectious diseases in limited-resource settings. Thus, the scope of the project precluded a full validation, and here we present abbreviated validation studies demonstrating adequate sensitivity, specificity, and reproducibility.

Here we describe baseline validation studies and field performance of a research-use-only chemiluminescent multiplex serology panel for measles, mumps, rubella, and varicella-zoster virus used with dried blood spots in support of the 2013–2014 Democratic Republic of the Congo Demographic and Health Survey. Characterization of the panel using U.S. FDA-cleared commercial kits shows good concordance for measles, mumps, rubella, and varicella-zoster with average sensitivity across assays of 94.9% and an average specificity of 91.4%. As expected, performance versus available standards validated for plaque-reduction assays does not provide a 1:1 correspondence with international units and yet demonstrates excellent linearity (average Hill’s slope = 1.02) and ∼4 logs of dynamic range. In addition, for the four assays, the multiplexed format allowed for inclusion of three positive and two negative controls for each sample. A prototype Dynex Multiplier chemiluminescent automated immunoassay instrument with a charge-coupled device camera provided a rugged and robust processing and data acquisition platform. Performance of a multiplex instrument for serological testing in a substantially resource-limited environment shows excellent reproducibility, minimal cross-reactivity, and a clear discrimination between specific assays and should be considered a viable option for future serosurveys.

IMPORTANCE The critical evaluation of immunization programs is key to identifying areas of suboptimal vaccination coverage, monitoring activities, and aiding development of public health policy. For evaluation of vaccine effectiveness, direct antibody binding assay methods, including enzyme immunoassay, enzyme-linked fluorescence assays, and indirect immunofluorescence assay, are most commonly used for detection of IgG antibodies. However, despite their well-demonstrated, reliable performance, they can be labor-intensive and time-consuming and require separate assays for each individual marker. This necessitates increased sample volumes, processing time, and personnel, which may limit assessment to a few key targets in resource-limited settings, that is, low- and middle-income locations where funding for public health or general infrastructure that directly impacts public health is restricted, limiting access to equipment, infrastructure, and trained personnel. One solution is a multiplexed immunoassay, which allows for the detection of multiple analytes in a single reaction for increased efficiency and rapid surveillance of infectious diseases in limited-resource settings. Thus, the scope of the project precluded a full validation, and here we present abbreviated validation studies demonstrating adequate sensitivity, specificity, and reproducibility.

Serosurveillance for vaccine-preventable diseases: A look inside the pertussis experience

INTRODUCTION

Serological surveillance (serosurveillance) provides the most direct measure of herd immunity of vaccine-preventable diseases. Little is known about the opportunities and challenges of serosurveillance experiences, particularly pertussis.

OBJECTIVE

To describe the process of serosurveillance for vaccine-preventable diseases with an emphasis on the experience of pertussis in the metropolitan area of Antioquia (Valle de Aburrá) in 2015 and 2016 and analyze the contributions and challenges for its sustainability.

MATERIALS AND METHODS

We described the planning and conduction of serosurveillance of pertussis antibodies of mothers and in the umbilical cord at the time of delivery in eight hospitals based on random sampling and their capacity to advance the serosurveillance periodically. We compared the contributions and the challenges of this experience with other probabilistic and non-probabilistic programs.

RESULTS

We achieved the participation of hospitals and mothers respecting the delivery care process. We established a serum bank following ethical and technical guidelines. This program based on the random selection of hospitals and mothers has enabled the estimation of antibodies prevalence in mothers and in the umbilical cord, which has been possible given the high coverage of hospital care during childbirth at a lower cost and fewer risks than a population-based survey in conflictive areas. The main challenges for the sustainability of this program are the creation of stable jobs and access to funding and legal and methodological long-term frameworks.

CONCLUSIONS

Hospital serosurveillance as described is an option to monitor the impact of vaccination on the population. Our experience could be reproduced in other regions under similar conditions if the above-mentioned challenges are solved.

Integrated Serologic Surveillance of Population Immunity and Disease Transmission

Antibodies are unique among biomarkers in their ability to identify persons with protective immunity to vaccine-preventable diseases and to measure past exposure to diverse pathogens. Most infectious disease surveillance maintains a single-disease focus, but broader testing of existing serologic surveys with multiplex antibody assays would create new opportunities for integrated surveillance. In this perspective, we highlight multiple areas for potential synergy where integrated surveillance could add more value to public health efforts than the current trend of independent disease monitoring through vertical programs. We describe innovations in laboratory and data science that should accelerate integration and identify remaining challenges with respect to specimen collection, testing, and analysis. Throughout, we illustrate how information generated through integrated surveillance platforms can create new opportunities to more quickly and precisely identify global health program gaps that range from undervaccination to emerging pathogens to multilayered health disparities that span diverse communicable diseases.

Measles and rubella serosurvey identifies rubella immunity gap in young adults of childbearing age in Zambia: The added value of nesting a serological survey within a post-campaign coverage evaluation survey

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We nested a measles and rubella serological survey in a vaccination coverage survey.

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Measles and rubella immunity was significantly higher than expected by vaccination.

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Study revealed immunity gap in young adults and risk of congenital rubella syndrome.

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Adding serology to a survey leveraged resources and provided complementary information.

Background

Serological surveys can potentially complement vaccine coverage surveys, such as post-vaccination campaign coverage evaluation surveys (PCES), by providing direct information on population immunity within and outside the target age range of the mass vaccination campaign. We estimate age-specific population immunity to measles and rubella viruses in Southern Province, Zambia, and assess the value of adding serological data to vaccination coverage estimates by nesting a serological survey within a PCES.

Methods

Dried blood spots (DBS) from fingerprick blood were collected from all individuals ages nine months or older in households participating in the PCES and tested for measles and rubella virus-specific immunoglobulin G (IgG) by enzyme immunoassay (Siemens Enzygnost, Marburg, Germany).

Results

Overall seroprevalence was 95.5% (95% CI: 92.8, 97.2) for measles virus-specific IgG and 97.7% (95% CI: 96.0, 98.7) for rubella virus-specific IgG. Rubella seroprevalence was 98.4% (95% CI: 95.9, 99.4) among children eligible for the MR vaccination campaign, significantly higher than the reported measles-rubella (MR) vaccination campaign coverage of 89.8% (p = 0.003), and higher than the 91.3% rubella seroprevalence for adolescents and adults 16–30 years of age (p = 0.049).

Conclusion

Seroprevalence to measles and rubella viruses in children younger than 16 years of age was significantly higher than expected from vaccination coverage estimates, likely reflecting exposure to wild-type viruses and underreporting of vaccination. The serosurvey revealed rubella immunity gaps among women 16–30 years of age, precisely the age group in which protection from rubella is most important to prevent congenital rubella syndrome. Nesting serological surveys within existing surveys can leverage resources and infrastructure while providing complementary information important to immunization programs.

Introducing new vaccines in low- and middle-income countries: challenges and approaches

INTRODUCTION

The number of new vaccine introductions (NVIs) in low and middle-income countries (LMICs) has markedly increased since 2010, raising challenges to often overstretched and underfunded health care systems.

AREAS COVERED

We present an overview of some of these challenges, focusing on programmatic decisions, delivery strategy, information and communication, pharmacovigilance and post-licensure evaluation. We also highlight field-based initiatives that may facilitate NVI.

EXPERT COMMENTARY

Some new vaccines targeting populations other than infants require alternative delivery strategies. NVIs impact upon existing supply chain management, in particular vaccines with novel characteristics. A lack of understanding about immunization and misconceptions may be detrimental to NVI, as well as insufficient or poorly trained health care workforce. Many barriers exist to achieving good vaccination coverage. Real-world evaluation of vaccine safety, effectiveness and impact in LMICs may be limited by lack of robust demographic and disease epidemiology data, as well as limited health care and surveillance infrastructure. A thorough planning phase is crucial to define the most suitable delivery strategy based on the vaccine's and country's specificities. A communication plan and social mobilization are essential. Implementation research and innovative approaches applied to logistics, delivery, communication and program evaluation can facilitate NVI.

Evaluation of measles immunity in Turkey: is it still a threat?

Background/aim

Measles is one of the important vaccine-preventable diseases with many complications in childhood. This study presents cross-sectional seroepidemiological data, beginning from neonatal cord blood in infants to children under 6 years of age, about waning of measles antibody and tries to suggest the proper time for measles immunization.

Materials and methods

A total of 564 blood samples consisting of neonatal cord blood and samples taken from infants and children at ages of 6, 9, 24–48, and 49–72 months were analyzed for measles seropositivity in a period of 6 months.

Results

Measles seropositivity rate was 72.5% in 109 cord blood samples, 2.6% in 117 infants of 6 months of age, and 3.6% in 111 infants of 9 months of age. Seropositivity was determined in 118 children at 24–48 months and in 109 children at 49–72 months and was 80.5% and 66%, respectively (P = 0.001). These children were vaccinated in the 12th month.

Conclusion

Though measles immunization coverage is 97% in Turkey, population immunity is somewhat lower than expected. Increases of measles cases in Europe and the refugee problem in the country could easily lead to outbreaks. Implementing the first dose of the immunization at 9 months may be an option.

Coverage and timeliness of vaccination and the validity of routine estimates: Insights from a vaccine registry in Kenya

BACKGROUND

The benefits of childhood vaccines are critically dependent on vaccination coverage. We used a vaccine registry (as gold standard) in Kenya to quantify errors in routine coverage methods (surveys and administrative reports), to estimate the magnitude of survivor bias, contrast coverage with timeliness and use both measures to estimate population immunity.

METHODS

Vaccination records of children in the Kilifi Health and Demographic Surveillance System (KHDSS), Kenya were combined with births, deaths, migration and residence data from 2010 to 17. Using inverse survival curves, we estimated up-to-date and age-appropriate vaccination coverage, calculated mean vaccination coverage in infancy as the area under the inverse survival curves, and estimated the proportion of fully immunised children (FIC). Results were compared with published coverage estimates. Risk factors for vaccination were assessed using Cox regression models.

RESULTS

We analysed data for 49,090 infants and 48,025 children aged 12-23 months in 6 birth cohorts and 6 cross-sectional surveys respectively, and found 2nd year of life surveys overestimated coverage by 2% compared to birth cohorts. Compared to mean coverage in infants, static coverage at 12 months was exaggerated by 7-8% for third doses of oral polio, pentavalent (Penta3) and pneumococcal conjugate vaccines, and by 24% for the measles vaccine. Surveys and administrative coverage also underestimated the proportion of the fully immunised child by 10-14%. For BCG, Penta3 and measles, timeliness was 23-44% higher in children born in a health facility but 20-37% lower in those who first attended during vaccine stock outs.

CONCLUSIONS

Standard coverage surveys in 12-23 month old children overestimate protection by ignoring timeliness, and survivor and recall biases. Where delayed vaccination is common, up-to-date coverage will give biased estimates of population immunity. Surveys and administrative methods also underestimate FIC prevalence. Better measurement of coverage and more sophisticated analyses are required to control vaccine preventable diseases.

Seroprevalence of Poliomyelitis Antibodies Among Children Aged 1 to 4 Years Old and Factors Associated With Poliovirus Susceptibility; Mexican Health and Nutrition Survey, 2012

Background

An essential component of the “Polio Eradication and Endgame Strategic Plan 2013–2018” is the evaluation of population immunity. Mexico introduced the inactivated polio vaccine (IPV) into its routine immunization schedule in 2007 but continued to give trivalent oral polio vaccine OPV twice a year during National Health Weeks through 2016.

Methods

To describe the seroprevalence of poliomyelitis among children one to four years old in Mexico and analyze risk factors for susceptibility. We detected antibodies to poliovirus type 1 by microneutralization test in 966 serum samples randomly selected from the National Health and Nutrition Survey, 2012. We assessed variables associated with susceptibility using multivariable logistic regression.

Results

The overall weighted seroprevalence of the general population was 98.39% (95% confidence interval [CI] 96.76–99.21). We found significant differences of prevalence according to age (94.39%, 95% CI 87.56–97.58; 99.02%, 95% CI 95.68–99.79; 99.82%, 95% CI 98.77–99.98; and 100% among children 1, 2, 3, and 4 years old respectively) and number of IPV doses (96.91%, 95% CI 90.55–99.44; 100%; 97.85%, 95% CI 94.46–99.18; and 99.92%, 95% CI 99.45–99.98 for 1 2, 3, and 4 number of doses, respectively). Multivariate analyses showed that susceptibility was associated with younger age, fewer doses of IPV, and certain socioeconomic levels.

Conclusions

Overall seroprevalence was high. However, we found susceptible children among younger ages and children with fewer or unknown IPV doses belonging to certain socioeconomic strata. Results are relevant for countries transitioning from OPV to IPV and underline the importance of achieving high coverage with IPV.

Integrating Blood Collection within Household Surveys: Lessons Learned from Nesting a Measles and Rubella Serological Survey within a Post-Campaign Coverage Evaluation Survey in Southern Province, Zambia

Age-specific population immunity to many vaccine-preventable diseases can be measured using serological surveys. However, stand-alone serological surveys are infrequently conducted in low- and middle-income countries because of costs, operational challenges, and potential high refusal rates for blood collection. Nesting a serosurvey within a household cluster survey may overcome some of these challenges. We share lessons learned from nesting a serosurvey within a measles and rubella vaccination post-campaign coverage evaluation survey (PCES). In 15 of the 26 PCES clusters in Southern Province, Zambia, we collected dried blood spots from 581 participants aged 9 months and older. Household participation rates for the main PCES were higher in the serosurvey clusters (86%) than PCES-only clusters (71%), suggesting that a serosurvey can be successfully integrated without adversely affecting PCES participation. Among households that participated in the PCES, 80% also participated in the serosurvey and 86% of individuals available in the household provided a blood sample for the serosurvey. Substantial planning and coordination, additional staff training, and community mobilization were critical to the success of the serosurvey. Most challenges stemmed from using different data collecting tools and teams for the serosurvey and PCES. A more efficient design would be to fully integrate the serosurvey by adding blood collection and additional questions to the PCES.

Revealing Measles Outbreak Risk With a Nested Immunoglobulin G Serosurvey in Madagascar

Madagascar reports few measles cases annually and high vaccination campaign coverage. However, the underlying age profile of immunity and risk of a measles outbreak is unknown. We conducted a nested serological survey, testing 1,005 serum samples (collected between November 2013 and December 2015 via Madagascar’s febrile rash surveillance system) for measles immunoglobulin G antibody titers. We directly estimated the age profile of immunity and compared these estimates with indirect estimates based on a birth cohort model of vaccination coverage and natural infection. Combining these estimates of the age profile of immunity in the population with an age-structured model of transmission, we further predicted the risk of a measles outbreak and the impact of mitigation strategies designed around supplementary immunization activities. The direct and indirect estimates of age-specific seroprevalence show that current measles susceptibility is over 10%, and modeling suggests that Madagascar may be at risk of a major measles epidemic.

Benefits and Challenges in Using Seroprevalence Data to Inform Models for Measles and Rubella Elimination

Background

Control efforts for measles and rubella are intensifying globally. It becomes increasingly important to identify and reach remaining susceptible populations as elimination is approached.

Methods

Serological surveys for measles and rubella can potentially measure susceptibility directly, but their use remains rare. In this study, using simulations, we outline key subtleties in interpretation associated with the dynamic context of age-specific immunity, highlighting how the patterns of immunity predicted from disease surveillance and vaccination coverage data may be misleading.

Results

High-quality representative serosurveys could provide a more accurate assessment of immunity if challenges of conducting, analyzing, and interpreting them are overcome. We frame the core disease control and elimination questions that could be addressed by improved serological tools, discussing challenges and suggesting approaches to increase the feasibility and sustainability of the tool.

Conclusions

Accounting for the dynamical context, serosurveys could play a key role in efforts to achieve and sustain elimination.

Current challenges and implications for dengue, chikungunya and Zika seroprevalence studies worldwide: A scoping review

BACKGROUND

Arboviral infections are a public health concern and an escalating problem worldwide. Estimating the burden of these diseases represents a major challenge that is complicated by the large number of unapparent infections, especially those of dengue fever. Serological surveys are thus required to identify the distribution of these diseases and measure their impact. Therefore, we undertook a scoping review of the literature to describe and summarize epidemiological practices, findings and insights related to seroprevalence studies of dengue, chikungunya and Zika virus, which have rapidly expanded across the globe in recent years.

METHODOLOGY/PRINCIPAL FINDINGS

Relevant studies were retrieved through a literature search of MEDLINE, WHOLIS, Lilacs, SciELO and Scopus (2000 to 2018). In total, 1389 publications were identified. Studies addressing the seroprevalence of dengue, chikungunya and/or Zika written in English or French and meeting the inclusion and exclusion criteria were included. In total, 147 studies were included, from which 185 data points were retrieved, as some studies used several different samples. Most of the studies were exclusively conducted on dengue (66.5%), but 16% were exclusively conducted on chikungunya, and 7 were exclusively conducted on Zika; the remainder were conducted on multiple arboviruses. A wide range of designs were applied, but most studies were conducted in the general population (39%) and in households (41%). Although several assays were used, enzyme-linked immunosorbent assays (ELISAs) were the predominant test used (77%). The temporal distribution of chikungunya studies followed the virus during its rapid expansion since 2004. The results revealed heterogeneity of arboviruses seroprevalence between continents and within a given country for dengue, chikungunya and Zika viruses, ranging from 0 to 100%, 76% and 73% respectively.

CONCLUSIONS/SIGNIFICANCE

Serological surveys provide the most direct measurement for defining the immunity landscape for infectious diseases, but the methodology remains difficult to implement. Overall, dengue, chikungunya and Zika serosurveys followed the expansion of these arboviruses, but there remain gaps in their geographic distribution. This review addresses the challenges for researchers regarding study design biases. Moreover, the development of reliable, rapid and affordable diagnosis tools represents a significant issue concerning the ability of seroprevalence surveys to differentiate infections when multiple viruses co-circulate.

Seroprevalence of Zika virus and Rubella virus IgG among blood donors in Rwanda and in Sweden

Seroprevalence studies provide information on the susceptibility to infection of certain populations, including women of childbearing age. Such data from Central Africa are scarce regarding two viruses that cause congenital infections: Zika virus (ZIKV), an emerging mosquito-borne infection, and Rubella virus (RuV), a vaccine-preventable infection. We report on the seroprevalence of both ZIKV and RuV from Rwanda, a country without any known cases of ZIKV, but bordering Uganda where this virus was isolated in 1947. Anti-ZIKV-specific and anti-RuV-specific immunoglobulin G (IgG) antibodies were analyzed by enzyme-linked immunosorbent assay (ELISA) in serum samples from 874 Rwandan and 215 Swedish blood donors. Samples positive for IgG antibodies against ZIKV were examined for viral RNA using real-time reverse transcription polymerase chain reaction (RT-qPCR). The seroprevalence of ZIKV IgG in Rwanda was 1.4% (12/874), of which the predominance of positive findings came from the Southeastern region. All anti-ZIKV IgG-positive samples were PCR-negative. Among 297 female blood donors of childbearing age, 295 (99.3%) were seronegative and thus susceptible to ZIKV. All Swedish blood donors were IgG-negative to ZIKV. In contrast, blood donors from both countries showed high seroprevalence of IgG to RuV: 91.2% for Rwandan and 92.1% for Swedish donors. Only 10.5% (31/294) of female donors of childbearing age from Rwanda were seronegative for RuV. In Rwanda, seroprevalence for ZIKV IgG antibodies was low, but high for RuV. Hence, women of childbearing age were susceptible to ZIKV. These data may be of value for decision-making regarding prophylactic measures.

Evaluation of nationwide supplementary immunization in Lao People's Democratic Republic: Population-based seroprevalence survey of anti-measles and anti-rubella IgG in children and adults, mathematical modelling and a stability testing of the vaccine

Background

Measles outbreaks have occurred in some countries despite supplementary immunization activities (SIA) using measles-containing vaccine with high vaccination coverage. We conducted a cross-sectional seroprevalence survey to estimate population immunity in Lao People's Democratic Republic where repeated mass immunization has failed to eliminate measles.

Methods and findings

In this nationwide multistage cluster sampling survey conducted in 2014 based on probability proportionate to size sampling, blood samples were collected from 2,135 children and adults living in 52 randomly selected villages. Anti-measles and anti-rubella IgG were measured, and IgG prevalence was calculated. We applied mathematical modelling to estimate the number of cases of congenital rubella syndrome (CRS) in 2013 that were averted by the 2011 SIA. A stability testing was applied to the MR vaccine at 4°C, 25°C, and 35°C to examine stability differences between measles and rubella vaccine components. Measles IgG prevalence was significantly lower in the target age groups (5–21 years) of the 2011 SIA using a combination vaccine for measles and rubella vaccine (MR vaccine) than in young adults (22–39 years) (86.8% [95% CI: 83.0–90.6] vs. 99.0% [98.3–99.8]; p<0.001), whereas rubella IgG prevalence was significantly higher (88.2% [84.5–91.8] vs. 74.6% [70.7–78.5]; p<0.001). In the SIA target age groups, prevalence of measles IgG, but not rubella IgG, increased with age. CRS cases prevented in 2013 ranged from 16 [0–50] to 92 [32–180] if the force of infection had remained unchanged or had been reduced by 75%, respectively. In freeze-dried conditions, the measles vaccine component was more heat sensitive than the rubella component.

Conclusions

Inconsistent IgG prevalence between measles and rubella in Lao PDR can be partly explained by different stability of the measles and rubella vaccine components under heat exposure. Suboptimal vaccine handling may cause insufficient immunogenicity for measles, which subsequently leads to an outbreak despite high SIA coverage, while direct evidence is lacking. Temperature monitoring of the vaccine should be conducted.

Serological Surveys for complementing assessments of vaccination coverage in sub-Saharan Africa: A systematic review

Background: Serosurveys of biomarkers of infection/vaccination are widely used for evaluating vaccine-induced immunity and monitoring the effectiveness of immunisation programmes in developed countries. In sub-Saharan Africa (sSA) where vaccination coverage (VC) estimates are often incomplete, inaccurate and overestimate effective population immunity, the use of serosurveys is limited. Methods: We conducted a review of the use of serosurveys to assess/complement assessments of VC in sSA by searching electronic databases (PubMed, Embase, Web of Science, Popline, Ovid and Africa Wide Information) for English language articles published from 1st January 1940 to 31st January 2017. We also searched the references of retrieved articles. SSA was defined as all of Africa excluding the countries in North Africa. We included only articles that measured VC and assessed the quality of these studies using the Newcastle-Ottawa Scale. Results: We found 1056 unique records, reviewed 20 eligible studies of which just 12 met our inclusion criteria. These 12 studies were serosurveys of measles, tetanus, polio and yellow fever. Antibodies induced by natural infection confounded serological test results and there was significant discordance between vaccination history and the presence of antibodies in all except for tetanus vaccine. No study looked at Hepatitis B. Conclusions: Serosurveys for tetanus or tetanus containing vaccines may be directly useful for ascertainment of vaccination exposure or reliably complement current survey methods that measure VC. Given the limited experience in using serosurveys for this purpose in sSA, well-designed serosurveys of tetanus and possibly hepatitis B are required to further validate/evaluate their performance.

Rabies Postexposure Prophylaxis Noncompletion After Dog Bites: Estimating the Unseen to Meet the Needs of the Underserved

Postexposure prophylaxis (PEP) prevents human rabies and is accessible in Cambodia principally in Phnom Penh, the capital. Timely, affordable access to PEP is a challenge for the mainly rural population. We aimed to identify districts independently associated with PEP noncompletion to position frontline vaccination centers. We analyzed the 2009-2013 database at the Rabies Prevention Center at the Institut Pasteur du Cambodge, Phnom Penh. Logistic regressions identified nongeographic determinants of PEP noncompletion as well as the districts that were independently associated with noncompletion after adjustment for these determinants. The influence of distance by road was estimated using a boosted regression-trees model. We computed a population attributable fraction (rabies index (RI)) for each district and developed a map of this RI distribution. A cartographic analysis based on the statistic developed by Getis and Ord identified clusters of high-RI districts. Factors independently associated with noncompletion were patients' district of residence, male sex, age 15-49 years, initial visit during rice harvest, the dog's status (culled or disappeared), and a prescribed PEP protocol requiring more than 3 PEP sessions (4 or 5). Four clusters of high-RI districts were identified using this analytical strategy, which is applicable to many vaccination or other health services. Positioning frontline PEP centers in these districts could significantly widen access to timely and adequate PEP.

Type A viral hepatitis: A summary and update on the molecular virology, epidemiology, pathogenesis and prevention

Although epidemic jaundice was well known to physicians of antiquity, it is only in recent years that medical science has begun to unravel the origins of hepatitis A virus (HAV) and the unique pathobiology underlying acute hepatitis A in humans. Improvements in sanitation and the successful development of highly efficacious vaccines have markedly reduced the worldwide prevalence and incidence of this enterically-transmitted infection over the past quarter century, yet the virus persists in vulnerable populations and remains a common cause of food-borne disease outbreaks in economically-advantaged societies. Reductions in the prevalence of HAV have led to increases in the median age at which infection occurs, often resulting in more severe disease in affected persons and paradoxical increases in disease burden in some developing nations. Here, we summarize recent advances in the molecular virology of HAV, an atypical member of the Picornaviridae family, survey what is known of the pathogenesis of hepatitis A in humans and the host-pathogen interactions that typify the infection, and review medical and public health aspects of immunisation and disease prevention.

Progress towards achieving and maintaining maternal and neonatal tetanus elimination in the African region

Despite the availability of effective tetanus prevention strategies, as of 2016, Maternal and Neonatal Tetanus Elimination (MNTE) has not yet been achieved in 18 countries globally. In this paper, we review the status of MNTE in the World Health Organization African Region (AFR),and provide recommendations for achieving and maintaining MNTE in AFR. As of November 2016, 37 (79%) AFR countries have achieved MNTE, with 10 (21%) countries remaining. DTP3 coverage increased from 52% in 2000 to 76% in 2015. In 2015, coverage with at least 2 doses of tetanus containing vaccine (TT2+) and proportion of newborns protected at birth (PAB) were 69% and 77%, compared with 44% and 62% in 2000, respectively. Since 1999, over 79 million women of reproductive age (WRA) have been vaccinated with TT2+ through supplementary immunization activities (SIAs). Despite the progress, only 54% of births were attended by skilled birth attendants (SBAs), 5 (11%) countries provided the 3 WHO-recommended booster doses to both sexes, and about 5.5 million WRA still need to be reached with SIAs. Coverage disparities still exist between countries that have achieved MNTE and those that have not. In 2015, coverage with DTP3 and PAB were higher in MNTE countries compared with those yet to achieve MNTE: 84% vs. 68% and 86% vs. 69%, respectively. Challenges to achieving MNTE in the remaining AFR countries include weak health systems, competing priorities, insufficient funding, insecurity, and sub-optimal neonatal tetanus (NT) surveillance. To achieve and maintain MNTE in AFR, increasing SBAs and tetanus vaccination coverage, integrating tetanus vaccination with other opportunities (e.g., polio and measles campaigns, mother and child health days), and providing appropriately spaced booster doses are needed. Strengthening NT surveillance and conducting serosurveys would ensure appropriate targeting of MNTE activities and high-quality information for validating the achievement and maintenance of elimination.

Vaccination coverage and immunization timeliness among children aged 12-23 months in Senegal: a Kaplan-Meier and Cox regression analysis approach

Introduction

Expanded programme on immunizations in resource-limited settings currently measure vaccination coverage defined as the proportion of children aged 12-23 months that have completed their vaccination. However, this indicator does not address the important question of when the scheduled vaccines were administered. We assessed the determinants of timely immunization to help the national EPI program manage vaccine-preventable diseases and impact positively on child survival in Senegal.

Methods

Vaccination data were obtained from the Demographic and Health Survey (DHS) carried out across the 14 regions in the country. Children were aged between 12-23 months. The assessment of vaccination coverage was done with the health card and/or by the mother’s recall of the vaccination act. For each vaccine, an assessment of delay in age-appropriate vaccination was done following WHO recommendations. Additionally, Kaplan-Meier survival function was used to estimate the proportion vaccinated by age and cox-proportional hazards models were used to examine risk factors for delays.

Results

A total of 2444 living children between 12–23 months of age were included in the analysis. The country vaccination was below the WHO recommended coverage level and, there was a gap in timeliness of children immunization. While BCG vaccine uptake was over 95%, coverage decreased with increasing number of Pentavalent vaccine doses (Penta 1: 95.6%, Penta 2: 93.5%: Penta 3: 89.2%). Median delay for BCG was 1.7 weeks. For polio at birth, the median delay was 5 days; all other vaccine doses had median delays of 2-4 weeks. For Penta 1 and Penta 3, 23.5% and 15.7% were given late respectively. A quarter of measles vaccines were not administered or were scheduled after the recommended age. Vaccinations that were not administered within the recommended age ranges were associated with mothers’ poor education level, multiple siblings, low socio-economic status and living in rural areas.

Conclusion

A significant delay in receipt of infant vaccines is found in Senegal while vaccine coverage is suboptimal. The national expanded program on immunization should consider measuring age at immunization or using seroepidemiological data to better monitor its impact.

A review of measles control in Kenya, with focus on recent innovations

Despite the existence of a highly effective measles vaccine and the decrease in worldwide deaths from measles by more than 79% from the 2000 baseline levels, measles today remains one of the leading causes of vaccine-preventable deaths in the world. The African region is a key player in the global fight against measles. Africa has made tremendous progress in its effort to immunize children and to control the disease, increasing its regional measles vaccination coverage from 56% in 2001 to 85% in 2010. The Republic of Kenya has been a strong follower of the World Health Assembly and Measles Elimination 2020 resolutions, which aims to eliminate measles from the country. Since the beginning of the 21st century, Kenya has faced many challenges, but also aid, in the form of new innovations, in their fight against measles. In 2002, Kenya started its first SIA using A-D syringes, and from 2003-2005, GAVI funded injection safety support (INS) to Kenya, as an effort to scale-up safe injection in sub-Saharan Africa. In 2016, the Kenya introduced Measles-Rubella (MR) combined vaccine in its nationwide SIA campaign, after recognizing that rubella is a disease that must be controlled along with measles. In 2009 and 2012 SIAs, Red Cross volunteers conducted H2H visits to promote immunization as well as document information from the community with regards to immunization, including the current coverage, to campaign management levels. Case-based surveillance, using real-time PCR, measles-specific IgM detection and Epi-link were used to confirm and map measles infection during outbreaks. Alternative serosurveys such as Dried Blood Spot and Urine sample surveys were also tested in Kenya. In 2013 and 2016, two studies were also conducted in Kenya on the use of SMS reminder system for routine immunization. These studies, which showed SMS to significantly improve the vaccination coverage, paved way for use of SMS in a larger scale in Kenya.

Seroepidemiology of whooping cough in the Czech Republic: estimates of incidence of infection in adults

OBJECTIVES

Despite widespread vaccination programmes, pertussis remains a significant health burden in many countries. Low awareness of the disease, the high rate of asymptomatic cases in adults and difficulties with diagnosis could explain the under-reporting of pertussis. The lack of data on actual incidence constitutes an obstacle for public health authorities for the implementation of a vaccination strategy against pertussis in adults. The aim of this study was to evaluate the seroprevalence of antibodies against Bordetella pertussis infection in adults and to estimate the actual incidence of the disease compared with the reported incidence.

STUDY DESIGN

Prospective, multicentre seroprevalence study.

METHODS

The study was conducted in 2000 adult subjects aged ≥18 years who had not received pertussis vaccination within the last 5 years. All enrolled subjects provided a blood sample for serum testing of IgG antibodies against pertussis toxin, performed by enzyme-linked immunosorbent assay, to indicate if they had an acute infection or if they had been infected with pertussis within the last 12 months or earlier. Results were validated in accordance with the guidelines of the European Sero-epidemiology Network 2 and were expressed in ESEN units/ml.

RESULTS

A positive concentration of anti-pertussis toxin antibodies, indicating previous pertussis infection, was demonstrated in 39.9% (n = 799) of all study subjects, and 0.40% (n = 8) of subjects had a concentration suggestive of a recent infection (within the last 12 months). The highest antibody seroprevalence was observed in subjects aged 18-29 years (1.46%). No cases of acute infection were detected.

CONCLUSIONS

During the study period, the reported incidence of pertussis in the adult population was 0.84/100,000 inhabitants. Based on the seroprevalence results from this study, it is estimated that the actual incidence of pertussis could be as much as 699/100,000 inhabitants. The actual incidence of pertussis in adults in the Czech Republic could therefore be at least 200-fold higher than the reported incidence. These findings support the need for pertussis vaccination in the adult population.

Assessing age-dependent susceptibility to measles in Japan

BACKGROUND

Routine vaccination against measles in Japan started in 1978. Whereas measles elimination was verified in 2015, multiple chains of measles transmission were observed in 2016. We aimed to reconstruct the age-dependent susceptibility to measles in Japan so that future vaccination strategies can be elucidated.

METHODS

An epidemiological model was used to quantify the age-dependent immune fraction using datasets of vaccination coverage and seroepidemiological survey. The second dose was interpreted in two different scenarios, i.e., booster and random shots. The effective reproduction number, the average number of secondary cases generated by a single infected individual, and the age at infection were explored using the age-dependent transmission model and the next generation matrix.

RESULTS

While the herd immunity threshold of measles likely ranges from 90% to 95%, assuming that the basic reproductive number ranges from 10 to 20, the estimated immune fraction in Japan was below those thresholds in 2016, despite the fact that the estimates were above 80% for all ages. If the second dose completely acted as the booster shot, a proportion immune above 90% was achieved only among those aged 5years or below in 2016. Alternatively, if the second dose was randomly distributed regardless of primary vaccination status, a proportion immune over 90% was achieved among those aged below 25years. The effective reproduction number was estimated to range from 1.50 to 3.01 and from 1.50 to 3.00, respectively, for scenarios 1 and 2 in 2016; if the current vaccination schedule were continued, the reproduction number is projected to range from 1.50 to 3.01 and 1.39 to 2.78, respectively, in 2025.

CONCLUSION

Japan continues to be prone to imported cases of measles. Supplementary vaccination among adults aged 20-49years would be effective if the chains of transmission continue to be observed in that age group.

Seroprevalence of Bordetella pertussis antibodies in adults in Hungary: results of an epidemiological cross-sectional study

Background

Pertussis (whooping cough) is well known to be underreported, particularly among adults, who can act as an infectious reservoir, potentially putting susceptible newborns at risk of serious illness. The purpose of this study was to estimate the seroprevalence of pertussis in adults in Hungary.

Methods

This epidemiological, cross-sectional study was conducted in adults in five general practitioners’ practices in Hungary. Serum anti-pertussis toxin immunoglobulin G (anti-PT IgG) antibody levels were analyzed using enzyme-linked immunosorbent assay. Sera were classified following manufacturer’s instructions as: strongly indicative of current/recent infection (≥1.5 optical density [OD] units); indicative of current/recent infection (≥1.0 OD units); seropositive (>0.3 OD units); or seronegative (≤0.3 OD units). Logistic regression was performed to describe the associations between seroprevalence and various characteristics.

Results

Between 24^th April 2014 and 24^th April 2015, 1999 adults (60.6% female; mean age 47.4 ± 17.7 years) were included in the analysis. A total of 14.8% were seropositive for anti-PT IgG, 1.1% had a level indicative of current/recent infection, and 0.1% had a level strongly indicative of current/recent infection. Logistic regression showed significant relationships between increased rates of seropositivity and: age ≥60 years (odds ratio [OR], 1.97; 95% confidence interval [CI], 1.39–2.80; p = .0002) or 18–29 years (OR, 1.67; 95% CI, 1.13–2.46; p = .0094) vs. 45–59 years; former smoker (OR, 1.46; 95% CI, 1.08–1.97; p = .014) or current smoker (OR, 1.38; 95% CI, 1.01–1.89; p = .045) vs. never smoker; and male (OR, 1.30; 95% CI, 1.01–1.68; p = .041) vs. female. Also, between increased rates of probable current/recent infection and current smoker (OR, 7.50; 95% CI, 2.32–24.31; p = .0008) or former smoker (OR, 4.07; 95% CI, 1.21–13.64; p = .023) vs. never smoker.

Conclusions

Approximately 85% of the adults studied were seronegative and therefore susceptible to pertussis infection. Approximately 1% had anti-PT IgG levels indicative of current/recent pertussis infection, which could potentially be transmitted to susceptible young infants. Vaccination of adults is a key way to indirectly protect infants.

Trial registration

Clinical Trials.gov NCT02014519. Prospectively registered 12 December 2013.